Three separate studies are proposed. The first study represents an extension of experiments already in progress to quantitate the dynamic ventilatory and cardiovascular responses of human bicycle ergometer exercise. Thus, the equipment is already available in the laboratory and has been proven suitable for experiments similar to those being proposed. Specifically, subjects will exercise on the bicycle ergometer with their end-tidal partial pressure of carbon dioxide maintained constant but slightly above the subject's resting value. This procedure reduces the input variation of carbon dioxide, hopefully to zero, to the respiratory center. These experiments will produce pulmonary transients to exercise in which the effect of variation in arterial CO2 on the chemoreceptors has been reduced to a minimum. This study will be repeated with the end-tidal CO2 allowed to fluctuate but with the inspired oxygen kept above 50%. Such a procedure will remove the effect of the peripheral chemoreceptors' sensitivity to oxygen by maintaining the oxygen component of the signal to the respiratory center constant. The second part of the study will incorporate the results of the present experiments as well as those proposed above into a mathematical model. This model will be designed to incorporate general knowledge of human physiology along with knowledge gained above concerning specific exercise responses and interactions of peripheral and central chemoreceptors into the dynamics of ventilation to different conditions during exercise. The third part of the proposed project represents a pilot study in the area of modeling long term whole body acid-base balance involving principally the respiratory and renal systems. The extent of development of this model will depend on available information and will be used to study integration techniques in simulation models and as a basis for further experimentation in the long term control of acid-base balance.